Chain saw

A chain saw, comprising:

• a main body
• a chain;
• a guide plate supported by and extending from the main body, the guide plate for supporting the chain with the chain rotating about the guide plate;
• a power output unit mounted within the main body and coupled to the chain, the power unit rotatable for driving the chain about the guide plate to cut a workpiece;
• and
• a locking device coupled to the guide plate and configured to tension the chain,
• wherein the locking device comprises:
• an operating member configured to be operated by a user to rotate about a first axis;
• a driving member configured to drive the guide plate to move relative to the power output unit to tension the chain around the guide plate;
• a first clutch coupling with the operating member and configured to rotate synchronously with the operating member;
• a second clutch comprising meshing teeth operably contacting a surface of the first clutch;
• and
• a limiting assembly coupled to a surface of the second clutch and configured to prevent the second clutch from rotating in a first direction about the first axis and allow the second clutch to rotate in a second direction about the first axis,
• wherein the driving member is connected with the second clutch so that the driving member is capable of rotating synchronously with the second clutch to drive the guide plate to move, each of the meshing teeth comprises a first sloped surface and a second sloped surface, an angle formed by an intersection of the first sloped surface and the first axis is smaller than an angle formed by an intersection of the second sloped surface and the first axis, the first clutch contacts the first sloped surface to drive the second clutch to rotate when the operating member rotates in the first direction, and the first clutch contacts the second sloped surface and crosses the second sloped surface when the operating member rotates in the second direction.